Thrombocytosis

Outline

Overview
Signalment
Signs
Causes and Risk Factors

BASICS

Overview

Increased peripheral platelet (thrombocyte) count usually >350 000/μL (>350 × 10⁹/L)
Usually secondary reactive thrombocytosis associated with chronic inflammatory/infectious diseases. Cytokines produced during an inflammatory response may stimulate megakaryopoiesis
Organ systems affected are associated with underlying cause
Primary thrombocytosis with myeloproliferative disorders
Physiologic thrombocytosis possible

Signalment

Although not pathologic, stallions and horses <3 years of age have higher platelet counts.

Signs

Specific signs are seldom observed and hemostatic function is usually normal. Hemorrhagic diathesis can occur if platelet function is abnormal (thrombocytopathia). Thrombosis may occur with platelet counts >1 000 000/μL
Signs will most likely relate to the primary underlying disease

Causes and Risk Factors

Primary Thrombocytosis

Occurs as a primary myeloproliferative disorder or associated with polycythemia vera
Yet to be diagnosed definitively in horses

Secondary (Reactive) Thrombocytosis

Physiologic causes include exercise/excitement (release of splenic platelet reserves)
Rebound phenomenon occurs after thrombocytopenia or hemorrhage
Immune-mediated hemolysis, including neonatal isoerythrolysis
Iron-deficiency anemia
Corticosteroid therapy
Chronic inflammatory/infectious conditions
Neoplasia
Musculoskeletal trauma
Splenectomy

Diagnosis ⬆ ⬇

Outline

Differential Diagnosis
CBC/Biochemistry/Urinalysis
Other Laboratory Tests
Imaging
Other Diagnostic Procedures
Pathologic Findings

DIAGNOSIS

Differential Diagnosis

Accurate history and complete physical examination should be used to localize (body system affected) and characterize (inflammatory, infectious, autoimmune, neoplastic, traumatic, physiologic).

CBC/Biochemistry/Urinalysis

Platelet counts of 401 000 to >1 000 000/μL (401–1000 × 10⁹/L) have been recorded
Other abnormalities related to underlying cause
Leukogram in combination with fibrinogen and globulins can help diagnose infectious, inflammatory, immune-mediated, and/or neoplastic (including myeloproliferative) diseases and changes associated with corticosteroid administration
Red blood cell morphology can help diagnose causes of anemia including chronic disease, iron deficiency, and hemolytic
Polycythemia may occur with splenic contraction, hemoconcentration, organ disease, or polycythemia vera
Changes in muscle enzymes, liver enzyme and function tests, and azotemia may occur related to primary disease
Hypoproteinemia/hypoalbuminemia may be associated with protein-losing enteropathy/nephropathy or effusive disorders

Other Laboratory Tests

Platelet function tests (automated platelet function analyzer; aggregometry; flow cytometry) for thrombocytopathia
Viscoelastic coagulation testing for hypercoagulability
Other abnormalities related to underlying disease
Further diagnostics for anemia include Coomb's testing and iron assays (blood and bone marrow)
Bone marrow aspirate cytology and immunophenotypic testing for myeloproliferative disorders

Imaging

Ultrasonography/radiography of the abdomen, thorax, and/or musculoskeletal system to identify/characterize underlying disease.

Other Diagnostic Procedures

Template or buccal mucosal bleeding time for thrombocytopathia
Cytology and culture of abdominal, thoracic, synovial fluid, and tracheal or bronchial samples
Percutaneous, rectal, or surgical aspirates/biopsies as indicated for underlying disease
Oral glucose absorption test for small intestinal malabsorption
Endoscopy of the airway/gastrointestinal tract

Pathologic Findings

Dependent on the underlying disorder.

Treatment ⬆ ⬇

TREATMENT

Specific treatment to reduce platelet count (i.e. plasmapheresis) is seldom indicated
The underlying disease process should be treated

Medications ⬆ ⬇

Outline

Drug(s) of Choice
Contraindications/Possible Interactions

MEDICATIONS

Drug(s) of Choice

Aspirin or clopidogrel antithrombotic therapy for hypercoagulability
In thrombocytopathia/bleeding tendencies fresh whole-blood or platelet-rich plasma transfusions may be indicated
Treatment of any underlying disease process

Contraindications/Possible Interactions

Avoid use of NSAIDs, especially aspirin, if there is evidence of platelet dysfunction.

Follow-up ⬆ ⬇

Outline

Patient Monitoring
Prevention/Avoidance
Possible Complications
Expected Course and Prognosis

FOLLOW-UP

Patient Monitoring

Hematologic monitoring as needed
Monitor response of underlying disease to treatment

Prevention/Avoidance

N/A

Possible Complications

Hemorrhagic diathesis with platelet dysfunction
Thrombosis and possible ischemic tissue damage (e.g. laminitis, organ dysfunction)

Expected Course and Prognosis

Dependent on successful treatment of underlying condition.

Miscellaneous ⬆ ⬇

Outline

Associated Conditions
Age-Related Factors
Zoonotic Potential
Pregnancy/Fertility/Breeding
See Also
Abbreviations

MISCELLANEOUS

Associated Conditions

N/A

Age-Related Factors

Young horses at increased risk.

Zoonotic Potential

N/A

Pregnancy/Fertility/Breeding

N/A

See Also

Abbreviations

NSAID = nonsteroidal anti-inflammatory drug

section name header

Basics ⬇

Diagnosis ⬆ ⬇

Treatment ⬆ ⬇

Medications ⬆ ⬇

Follow-up ⬆ ⬇

Miscellaneous ⬆ ⬇

Suggested Reading ⬆ ⬇

Author(s) ⬆